Is it possible for someone to break into my iPhone?

I left my iPhone in a Hong Kong taxi (I didn't ask for a receipt and don't know the taxi number or driver). My have it set so that it requires my 4-digit pass code every time, but is it possible for whoever has my phone to access my email and other information by hacking or jail breaking it? Should I be changing my passwords for everything?

You should use the "find my phone" app and delete all data